Production of alkali metal carbamates



Patented Aug. 7, I934 me ories? or ALKALI METAL v ARBAMATES i Robert Burns MacMullin Niagara-trails, N. Y.; assignor to The'Mathieson Alkali Works; Inc.) New York, N. Y.; incorporation of: Virginia No Drawing. 1. Application Apriljli,1934, S'erialNo., 'ZlQ,3l a

Claims." (cree -41g I This invention relates to improvementsin the separated and removed while maintaining the production ,of alkali-metal carbamates; from concentration of. theaqueous ammonia. solualkali-metal bicarbonates. The present inven :tion at 01 :upwards (by weight) of- NH3. tion is an improvement in the invention dis- The: separation." may be accomplished by filtra- 5 closed in application Serial No. 692,398, filed tion, for example, or by any other suitable 160 March 31, 1932, by GeorgeL. Cunningham, means; Wesley K. McCready and ,myself which has .Theifollowing examples will illustrate the in- .matured into PatentNo. 1,964,723, dated July vention: z x I 3, 1934. 1 Equalspartsby weight of KHCOaahd an- '..='10 In carryingout the invention described in hydrous :NH's" were reacted together at a temthat prior application for the production of .-.perature of 50? (LL-and an absolutepressurebf sodium carbamatefor example-sodiumbicar- '287 pounds per square inch. After reaction, bonate is subjected to treatment with-anhydrous thetmother liquor comprised about 50% water. ammonia or with an aqueous. solution of am- The-.yieldconsisted. of about 94%-KCO2NH2.H2O

-16 monia containing from 35-50% to 100%,;as a and i.,6%.=.=KHCO3. Filtration .Jwas 'efiected at limit NHa Concentrations of about 7:99% ,50..sC.'-. a.

NH; are particularly advantageous. I'he reac '.'-2.-=Equal= parts byweight of KHCO3 and an- ..tion proceeds as follows: 7 r i --hydrous -NH3' were reacted-together. at a temv,perature'of: 70 -C. and an absolute pressure of z 478 .pounds..per.square inch. .The reaction took If the concentration of the aqueous ammonia -u j g solution is too low, sodium sesqui .carbonate Percent will form instead of sodium carbamate. This :KCOZNHZ v2.0

lower limit approximates 35%"NH3. Other 23.5 25 ammonia-containing salts are a1so-formed,.in *KZCO3 4.5

some cases .with NR3 concentrations justiiabove I V I 35%. With anhydrous ammonia or with the 3Af-ter reaction, the 'mother' liquor contained higher concentrationsof aqueous ammonia, the about 20% "Hz O. Filtration was effected at 70 reaction proceeds but very slowly- The-i'nven- C'- 'l'lo-absolute'pressure'at the endof the re- 30 'tion there described is applicable with particular action was about 417 pou d p Square 'inch/ advantage 'to' crude ammonia soda; iurther, 3. NaHCOs andanhydrous N'Hs, equal parts by when the concentrationof the aqueous ammonia eight,*Were ra'cted to a d solution becomes too low, its remaining (3'. After reaction, the mother liquor contained ammonia content may: be recoveredby distil- 1% 20- e yields consisted of 88 to- 35 lation. r -9'l%- nacoznnz-with1 from1 3 to 12% uncon- I have now discovered that if the invention vel'ted' l laHCOe. Filtration was e'fiected at 50, described in the aforesaid application iscarried '70"and'90" C. respectively. The absolute pres- Out at temperature upwards of 50920., advansures at'thestart-of the reactions were 287, 4'78 tages as to conversion and the time required and-738-pouhds per square inch respectively and for reaction are to be obtained. These advanattheen'd-of about 250, 417 and 643 poundsper tages include, (1) speeding of the'time required 'squareinch respectively.

- for reaction, and (2) good conversion; As here- The proportions of the reacting materials are inafter noted, while the present invention" is 'not' critical. 'An' excess of ammonia is desirable, of advantage in the formation ofthecarba- "however, as' carbamate formation is promoted mates of the alkali metals generally it is parby- 'excessNHa. High initial concentrations of ==Z00 ticularly so in the case-of potassium; -Tempera- NHe- -are advantageous. Concentrations of "75- tures of 50 C. to 90 C. are particularly ad- A 95% NH: (by weight), for example, are advanvantagecus. ptageous i According to the present invention the As the-nature of the product depends on the 5 50 bicarbonate of the alkali-metal, thecarbamate final condition'at-the time of separation, care 1-195 of which isdesired, sodium or potassium bi- 'ShOl11d'- b6' taken that proper-conditions are carbonate, for example, is subjected to treatmaintained at theatime of separation. To illusment with anhydrous liquid ammonia :or an trate, if the concentration oftheaqueous amaqueous solution of ammonia at a temperature -monia. solution is-too low, compounds other than -56 upwards of 50 C. and the carbamate formed Zthatdesired-Will be-iormed- In thecase of so--* 7 aqueous ammonia solution is too low, sodium -ed than those for sodium carbamate. vention accordingly is of particular benefit in sesquicarbonate will form instead of sodium carbamate. This lower limit approximates 35% NHs. Other ammonia-containingsalts are also formed, in same cases, with NH3 concentrations just above 35%. Difiiculties due to too low an ammonia concentration may be avoided by maintaining the NI-Is concentration at 35%. or

upwards.

With reference to the concentration of the aqueous solution of ammonia, it should be'noted that since water is evolved in the reaction attending the formation of the carbamate the. concentration of H20 in the NH: at" the time of separation will depend on the proportion of NaHCO; to NH: originally brought together, as

well as the initial concentration of H20 in the NI-Is used. Thus, if equal parts by weightof dry NaHCOs and anhydrous NH: are reacted, the

motherliquor will contain-21.2% H20 and 78.8% NHs.

Care should be taken that the above factors are properly coordinated so as to maintain the concentration of NH: at 35% or upwards by weight. Y

Again the nature of the product depends upon the temperature atwhich the separation is .ef-

fected. Thus if the reaction be carried out at 70 C., for example, and the mixture cooled down to, a temperature of nearly -30 C., by flashing off :NHa, and the mixture filtered, both KCOzNI-Iz and NaCOzNI-Iz form ammoniates. That is, they take on ammonia of crystallization. 0n warmting, these ammoniates dissociate, leaving the carbamate alone. Again, if the temperature of separation is 150 C. or over carbimides result, along with, carbonates and cyanates. If however, the filtration is performed at 0 to 90 C. .for example, or 0 to 70 C., the carbamates result direct. These ranges are, of. course, subject to considerable latitude, but for practical. reasons, one would not want to filter much below 0 C. (because .of ammoniate formation, necessitating NH3 recovery) or above 100 C. (necessitating apparatus capable of withstandingv about 1,000 pounds per square inch pressure).

While temperatures from C. to 90 C. have been stated to be particularly advantageous, it is to be understood that theinvention contemplates the use of temperatures higher than 90 C. At temperatureshigher than those recommended, the carbamate will form but its formation is accomplished along with the formation of other compounds; the amount of the contamination being'determined partly by the temperature employed and partly by the length of the heating. Temperatures higher than ISO-180C. are not recommended as somedecomposition of the carbamate takes place at these temperatures.

Conditions for the formation of potassium carbamatefree from by-products are more restrict- The indisclosing satisfactory conditions for the formation of KCO2NH2. Best results, in the case of KCO2NH2, appearto, be obtained when the reaction is conducted at a temperature from 50- C., followed by separation at a temperature from 040 C. If these conditions are observed,

a minimum decomposition to K2003 is secured.

cessary to securegood conversion at the conditions selected; Reaction to. form the'carbamate desired may be promoted by securing goodcontact between the reactants. This contact may of ammonia containing about 35-100% formed at a temperature of,0-70 C.

be secured, in conventional manner, by stirring;

mixing or other appropriate form of agitation. While the invention has been described with particular reference to the carbamates of sodium and potassium by usingthe other alkali-metal bicarbonates the correspondingallgaliemetal carbamates may be produced.

I claim:

1. In the production of alkali-metal carbamates from alkali-metal bicarbonates, the improvement which comprises subjecting the bicarbonate to treatment with an aqueous solution y weight of, NH3 at a' temperature upwards of 50 C.v

2. In the production of alkali-metal carbamates from alkali-metal bicarbonates, the improvement which comprises subjecting the bicarbonate to treatment with an aqueous solution of ammonia containing about 35100% by weight of NI-Ia at a temperature upwards of 50 C;, and separating the carbamate thus formed while maintaining the concentration of the aqueous ammonia solution'at 35% orupwards of -NH3. a i 3. In the production of sodium carbamate from sodium- *bicarbonate, the improvement which comprises subjecting the bicarbonate to treatment with an aqueous solution of ammonia containing about 35-'-100-%' by-weight of NH3 at a temperature upwards of 50-C.: J:

4: In the production of potassium carbamate from potassium bicarbonate, the" improveinent which comprises subjecting the bicarbonate to treatment with an aqueous solution of ammonia containing about 35-100% by weight of- NH; at a-temperature upwards of 50 C.- r

5. In the production of alkali-metal carbamates from alkali-metal bicarbonates, the improvement which comprises subjecting the bicarbonate to. treatment-with an aqueous'solu- .tion of ammonia containing-about 35-100% by Weight of NH3 at a temperature of BO -90 .C.

6.'In the production of alkali-metal carbamatesv frompalkali-metal bicarbonates,- the improvement which comprises subjecting/the bicarbonate to treatment with an aqueous solution of ammonia containing about 35-100%'- by weight of NH; at a temperature upwards of 50 C.,v and separating the. carbamate thus 7.'Inp the productionof-alkali-metal carbamates. from; alkali-metal .bicarbonates, the; improvement which comprises subjecting the bicarbonate to treatment with an aqueoussolu- .tion of ammonia containing about 35-100%. by. weight of NH3 at a' ,temperature upwardsof 50 C., and separating the carbamate, thus formed at a temperature of .O".-'70 C., while maintaining the concentration of ;the aqueous ammonia solutionat 35% or upwards of NH 8. In the production of alkali-metal carbamates .from alkali-metal bicarbonatea; -,the

improvement which comprises subjecting the bicarbonate totreatment with an aqueous solution of ammonia containing about 35100% by weight of NH3 at a temperature of 50-90" C.,

and separating the carbamate thus formed while maintaining the concentration of the aqueous ammonia solution at 35%, or upwards of NHs. The reaction should be continued as long as ne- 9. In the production of sodium carbamate from sodium 7 bicarbonate, the (improvement vwhich comprises subjecting the bicarbonate .to treatment with an aqueous solution-of ammonia containing about 35-100%. by weight of NH3, at

a temperature upwards of 50 C., and separating the carbamate thus formed while maintaining the concentration of the aqueous ammonia solution at 35% or upwards of NH3.

10. In the production of potassium carbamate from potassium bicarbonate, the improvement which comprises subjecting the bicarbonate to treatment with an aqueous solution of ammonia containing about 35-100% by weight of NH; at a temperature upwards of 50 C., and separating the carbamate thus formed while maintaining the concentration of the aqueous ammonia solution at 35% or upwards of NH3.

11. In the production of alkali-metal carbamates from alkali-metal bicarbonates, the improvement which comprises subjecting the bicarbonate to treatment with an aqueous solution of ammonia containing about -95% by weight of NH3 at a temperature upwards of 50 C.

12. In the production of alkali-metal carbamates from alkali-metal bicarbonates, the improvement which comprises subjecting the bicarbonate to treatment with an aqueous solution of ammonia containing about 75-95% by weight of NH3 at a temperature upwards of 50 C., and separating the carbamate thus formed while maintaining the concentration of the aqueous ammonia solution at 35% or upwards of NH3.

13. In the production of alkali-metal carbamates from alkali-metal bicarbonates, the improvement which comprises subjecting the bicarbonate to treatment with an aqueous solution of ammonia containing about 75-95% by weight of NH3, at a temperature of 50-90 C. a

14. In the production of alkali-metal carbamates from alkali-metal bicarbonates, the im- 

